The present invention ralates to the deflection yoke, particularly the precision deflection yoke suitable for high precision television sets, cathode-ray tube (CRT) display unit, etc.
As well known, the color cathode-ray tube in which three electron guns are arranged in-line is generally employed in the television receiver sets, video monitors, CRT display units, etc. The delection yoke which is mounted on the cathode-ray tube for deflecting the electron beams is constructed so that the horizontal deflection coils generate a pincushion type deflection magnetic field as a whole and the vertical deflection coils generate a barrel type deflection magnetic field. Thus, the misconvergence can be theoretically eliminated by constructing the deflection yoke as described above. However, it is difficult to materialize the theoretical deflection magnetic field due to the construction of the cathode-ray tube, for example, the curvature of the fluorescent scope and the tilt of the electron beams, dimensional error in the assembly workmanship during manufacturing, and the construction of the deflection yoke, for example, the impossibility of obtaining a desired conductor distribution of the deflection coil in the manufacturing processes.
Accordingly the misconvergence actually takes place in various types of patterns. For example, if the electron beams are deflected by the deflection magnetic field described above as shown in FIG. 1, a cross misconvergence PQv is caused at a position in the Y-axis direction on the screen and a paraboloidal misconvergence X.sub.H is caused at a position in the X-axis direction.
Conventionally, the deflection magnetic field is corrected for eliminating the misconvergence by changing the conductor distribution of the deflection coil through design modification or by generating the correction magnetic field with a permanent magnet or a magnetic element attached to the deflection yoke. However it is difficult to eliminate the cross misconvergence PQv. Moreover, since the amount of misconvergence differs with the cathode-ray tube and the deflection yoke which are to be combined, the pattern of correction should be determined for each type of combination. Therefore the yield rate of the deflection yoke cannot be effectively improved; particularly, as to the cathode-ray tube for displaying the characters, the yield rate of the deflection yoke more deteriorates since the permissible range or error is small.